In a small saucepan, boil the orange juice and vinegar until reduced to about 1/3 cup; reserve off heat.
Heat the oil in a big nonstick skillet and cook fish 3-4 minutes per side or until it is golden brown on the outside, opaque but still moist inside and just barely flakes when tested with a fork.
Season with salt and pepper; remove fish to a serving platter.
Add the tequila to the skillet and bring to a boil, scraping up any browned bits; add the reserved orange juice reduction to the same skillet and bring to a boil.
Immediately decrease the heat to low and add the butter, 1 piece at a time, whisking just until melted.
Remove from heat and stir in the cilantro; spoon sauce over the fish; serve immediately.